1. Field of the Invention
The present invention relates to a pneumatic vehicle tire, more specifically relates to a pneumatic vehicle tire which improves the running performance on ice and snow, in particular, the running performance on ice and snow at initial and with the elapse of time, while maintaining the good wear resistance (or without substantially reducing the wear resistance).
2. Description of the Related Art
In the past, when driving a car in the winter season in areas with large snowfall, use has been made of tires with spikes embedded in them, i.e., spiked tires, or snow chains are attached to the tires, so as to ensure safety when driving on snow- and ice-covered roads. Spiked tires and snow chains, however, tend to cause wear and damage to the roads, and as a result, dust and causing air pollution are created, and major environmental problems are caused. To resolve these safety and the environmental problems, the use of studless tires which have braking ability and traction on snow- and ice-covered roads, without the use of spikes and chains, is rapidly spreading.
As such studless tires, there have been proposed tires with treads obtained by mixing into the matrix rubber a low hardness vulcanized rubber composition with a high adhesive effect (i.e., an ability of the tread surface to contact the ice-covered road surface and follow the shape of the same) so as to improve the frictional force on the ice (see Japanese Unexamined Patent Publication (Kokai) No. 63-92659, Japanese Unexamined Patent Publication (Kokai) No. 63-172750,Japanese Unexamined Patent Publication (Kokai) No. 4-38209, Japanese Unexamined Patent Publication (Kokai) No. 3-10907, etc.)
Japanese Unexamined Patent Publication (Kokai) No. 63-92659 discloses a pneumatic vehicle tire containing a soft vulcanized rubber powder having a glass transition point of no more than -50.degree. C. and a particle size of 1000 .mu.m or less. However, the adhesive effect of this matrix rubber is not sufficient and the performance thereof on ice is not necessarily satisfactory.
On the other hand, Japanese Unexamined Patent 10 Publication (Kokai) No. 60-139503 discloses a studless tire using tread rubber containing high hardness rubber particles. However, the adhesive effect of the rubber particles themselves was low, and therefore, the performance on ice was not necessarily satisfactory.
Further, Japanese Unexamined Patent Publication (Kokai) No. 4-38209 discloses the compounding of low hardness rubber particles and short fibers. However, the diameter of the rubber particles was relatively large, and therefore, the wear resistance and the mixing and processing ability were insufficient. Further, Japanese Unexamined Patent Publication (Kokai) No. 3-10907 proposes the compounding, to the matrix rubber, a low hardness preliminalily vulcanized rubber composition having an average particle size of 0.5 to 3 mm so as to improve the performance on ice. However, this pneumatic vehicle tire also is insufficient in the adhesive effect of the matrix rubber and the performance on ice is not necessarily satisfactory.
As mentioned above, the prior art had the problem that the frictional force on ice is not sufficient and the mixing and processing ability are poor.